His hands grew heavy (his eyes grew heavy)
He grew weak. His hands weakened.
("And Moses' hands were heavy. And they took a stone and put it under him, and he sat upon it, and Aaron and Hur supported his hands, one on the one side, and the other on the other side. And his hands were steady until the going down of the sun" - Exodus 17:12, about Moses during the battle with Amalek)
Translation
Expression (Hebrew)
כָּבְדוּ יָדָיו (כָּבְדוּ עֵינָיו)
Definition (Hebrew)
נֶחְלַשׁ כּוֹחוֹ. נֶחְלְשׁוּ יָדָיו.
("וִידֵי מֹשֶׁה כְּבֵדִים. וַיִּקְחוּ אֶבֶן וַיָּשִׂימוּ תַחְתָּיו וַיֵּשֶׁב עָלֶיהָ וְאַהֲרֹן וְחוּר תָּמְכוּ בְיָדָיו מִזֶּה אֶחָד וּמִזֶּה אֶחָד. וַיְהִי יָדָיו אֱמוּנָה עַד בֹּא הַשָּׁמֶשׁ"- שְׁמוֹת יז יב, עַל מֹשֶׁה בִּזְמַן הַמִּלְחָמָה עִם עֲמָלֵק)